The present invention concerns improvements in and relating to monitoring and/or detecting and particularly, but not exclusively, to monitoring items such as pipes, for alpha source contamination.
Any item which passes time within the active area of a nuclear facility may become contaminated by radioactive material from within that area. As a result, before the item can be removed and subsequently re-used, disposed of or recycled, its potential contamination needs to be evaluated.
The absence of contamination may allow an item to be re-released. The higher grade of waste items are categorised as, the greater the storage/disposal costs which apply to their decommissioning.
It is therefore important to check the level of contamination in order to appropriately and cost effectively dispose of the item.
Detection and monitoring of alpha contamination of such items presents a number of difficulties, principally due to the short distance over which alpha particles can be detected. Alpha particles are stopped by tens of micrometers of solid material and within a few centimetres in air. Detectors further away in these distances cannot detect the alpha contamination.
In certain scenarios this, therefore, makes the detection of the alpha contamination very difficult, calling for close proximity scanning of the article with a detector.
In other scenarios, such detection is physically impossible as the inside surfaces of, for example, pipes, scaffolding and ducts are simply not accessible to such detectors and yet the detectors cannot monitor the alpha contamination through the walls of such items.
With any it can be useful to be able to locate the position of a source of contamination. Such information may allow more accurately controlled subsequent decontamination to take place or may also allow the item to be cut into one or more pieces some of which are substantially free from contamination and may thus be more easily disposed of.
The present invention aims to provide apparatus and methods for the monitoring of items for alpha contamination, and also to provide information relating to the position of the alpha contamination within or on the item. Systems for evaluating the position of other forms of contamination are also provided.
According to a first aspect of the invention we provide a system for monitoring alpha emitting sources on an item/location, the item/location being in contact with a medium, alpha emissions generating ions in the medium, the system comprising an instrument having a detecting chamber, the detecting chamber being provided with one or more electrodes for discharging ions, the instrument further being provided with means to monitor ions discharged on the electrode(s) to generate discharge with time data, the system being provided with means for moving the medium from in proximity to the item/location through the detecting chamber in a controlled manner, the discharge monitoring means monitoring the discharge occurring with time, the instrument being provided with processing means for converting the discharge with time data into alpha source position on the item/location data.
The item(s) to be monitored may be or include tools, pipes, pumps, filters, cables, beams, rods and the like, but particularly elongate items. The locations may include surfaces in general, such as floors, walls, ceilings, soil, rubble, material on a conveyor, and include parts of, or surfaces of items, such as glove boxes, tanks, vessels and the like.
Preferably the item is mounted or supported so as to maximise the surface area exposed, for instance to the medium flow.
The item or location may be introduced within the detecting chamber.
The item or location may be monitored in-situ. The item or location may be connected to the detecting chamber by medium conveying means, such as a pipe or conduit. The conveying means may be temporarily connected to the item or location. The conveying means may be provided as a part of the instrument. The conveying means, item or location and detecting chamber may define a closed circuit.
The medium may be a fluid, such as a liquid, but is preferably a gas. The gas may be a mixture, such as air, or may be in substantially single gas form, such as argon.
The detecting chamber may comprise an elongate chamber. The detecting chamber may have a circular or rectilinear cross-section.
The detecting chamber may be provided with an inlet and an outlet, the electrodes being provided between the inlet and the outlet. The inlet and/or outlet may connect to the surrounding environment for the instrument, for instance to give an open circuit instrument. The inlet and/or outlet may connect the instrument to the item or location, for instance through intermediate fluid conveying means, for instance to give a closed circuit.
Preferably means are provided within the system to remove extraneous ions and/or particulate matter. The ions and/or particles may be removed by a filter. A filter may be provided between downstream of the electrodes. The filter may, for instance be provided in the medium conveying means prior to the item or location. A filter is preferably provided in this way in a sealed system.
Particularly in an open system, a filter may be provided between the inlet from the surrounding environment and the item or location and/or detecting chamber. A filter may be provided between the detecting chamber and the outlet to the surrounding environment.
The detecting chamber may be openable to introduce or remove an item or location, for instance for an open circuit. The detecting chamber may comprise a sealable chamber, for instance for a closed circuit. The seal may be broken to make the chamber accessible to introduce and/or remove an item to be monitored.
Preferably the item or location is positioned upstream in the medium flow relative to the electrodes, where medium flow is used to move the ions.
The instrument may be provided with a single electrode. The instrument may be provided with a charged element or plate, such as an electret.
Preferably the detecting chamber is provided with a plurality of electrodes, the electrodes being spaced from one another. The electrodes may be configured with a first outer electrode and a second outer electrode and none or one or more intermediate electrodes provided there between.
The electrodes are preferably arranged parallel to the direction of medium flow. Preferably the medium flow passes through the spacing between the electrodes.
One or more, and preferably all, of the electrodes may be planar. Preferably the electrodes are provided parallel to one another. Preferably the electrodes are provided in opposition, for instance, an outer electrode being opposed by one electrode, an intermediate electrode being opposed by two electrodes. The spacing between the electrodes is preferably the same between each pair of opposing electrodes. The spacing between the outer electrodes and the detector chamber is preferably the same as between opposing electrodes.
The electrodes may be continuous, such as a plate, or discontinuous, such as a grid.
An applied, preferably externally generated, potential may be employed. The electrical potential is preferably provided by an external power source. An electrostatic potential may be employed, for instance from a charged plate or element, such as an electret.
Potentials of between 10 V and 1000 V may be provided.
The means for monitoring ions discharged and/or collected on the electrode(s) may comprise electrostatic charge monitoring means. More preferably the means for monitoring ions discharged on the electrode(s) comprise current indicating means and more preferably current measuring means. Preferably a single current measuring means is used. Preferably the combined current of all the electrodes connected to the current measuring means is measured. An electrometer, and most preferably a ground referenced electrometer is preferred for this purpose.
The means for moving the medium may comprise a piston provided in a bore in fluid connection with the detector chamber. The piston may be provided upstream or downstream of the detector chamber.
The means for moving the medium may be a fan. A removable obstruction to medium flow, such as a chopper or shutter, may be provided. The fan may be of controllable, and preferably of variable, speed. The electrodes may be provided between the medium moving means and the item or location, particularly for a fan.
The means for moving the medium may move the medium within a closed or open circuit.
The medium may pass over the item/location, pass the electrode(s) and then be returned upstream of the item/location. In a closed circuit the provision of means to remove ions, after passing the electrode(s) and prior to returning to the item/location is preferred.
The medium may pass over the item/location, pass the electrode(s) and be exhausted to the environment of the instrument. The medium is preferably filtered after passing the electrode(s) in such a case to remove particulate material. The medium may pass to a reservoir after passing the electrode(s).
The medium may be drawn from the environment prior to passing the item/location. Preferably in such a case the medium is filtered prior to passing the item/location to remove pre-existing ions.
The medium may be moved between the item/location and the electrodes such that laminar flow occurs, but non-laminar flow may be used. Preferably the medium is moved between the item/location and the electrode(s) such that the medium passes the electrode(s) in the same order as it passes the item/location.
One or more discrete flow paths over a surface or surfaces of the item or a location may be provided. A pipe, for instance, may have an external flow path separated from an internal flow path by the material forming the pipe. Preferably means are provided for regulating the medium flow along one or more of the discrete paths. Detection of alpha sources on or in one more of the discrete paths alone may be provided by obscuring or inhibiting one or more of the other flow paths. sealing means may be provided to inhibit flow along one or more of the flow paths, most preferably in a selective manner. Inflatable seals and/or iris seals and/or aperture seals may be provided.
The processing of discharge against time data to alpha source position data may be effected by equating the sequence of fluid passing the electrodes, and hence the sequence of the discharge signal, with the sequence of positions on the item/location the fluid passes. The process may equate the signal at a point in time with a position in the system from which the fluid will have moved in the elapsed time from fluid movement start. The relationship of time to position preferably incorporates a function representative of the fluid flowrate within the system.
Means may be provided for measuring the flowrate within the system, and particularly between the item/location and the electrodes.
Means may be provided for reversing the flow of medium through the system between monitoring runs. The medium flow means may be reversed in their direction. The connections between the detector chamber and the item/location may be reversed. The item/location may be reversed within the instrument.
One or more electrodes may be provided on both sides of the item/location. In one medium flow direction one of the electrode(s) may act as an ion filter and the other electrode(s) as the detectors, in the other medium flow direction the roles may be reversed.
According to a second aspect of the invention we provide a method for monitoring alpha emitting sources on an item/location, the method comprising contacting the item/location with a medium, alpha emissions generating ions in the medium, moving the medium to a detecting chamber provided in an instrument in a controlled manner, the detecting chamber being provided with one or more electrodes for discharging and/or collecting ions, the method further comprising monitoring ions discharged on the electrode(s) to give discharge against time data, the method including processing the discharge against time data to give alpha source position data.
The second aspect of the invention includes the features, options and possibilities set out elsewhere in this application, including the steps necessary to implement them.